We perform a projection study for the sensitivity of the upgraded CMS detector to new physics in a mono-Higgs sector, h bb plus missing transverse momentum final state, at the HL-LHC. The focus lies on signals with boosted Higgs bosons, resulting in a large radius jet containing both b quarks that can are identified as originating from a Higgs boson. The search is sensitive to a variety of BSM models and in this analysis the results are interpreted in terms of 2HDM+a model. We find that with a data set corresponding to 3000 fb, masses from 750 to 2000 GeV could be excluded for GeV and masses from 1250 to 1600 GeV could be excluded for GeV. The 2HDM+a signals with and GeV, which are not yet excluded, could reach a significance near 5.